The present invention relates to a plasma processing apparatus and a plasma processing method use in processes of manufacturing a semiconductor device and the like.
Recently, rapid progress in performance, integration and miniaturization of semiconductor devices is being achieved. For the purpose of achieving higher integration of semiconductor devices, microfabrication techniques, epitaxial growth techniques, packaging technology and the like need to be improved. Among them, microfabrication techniques have great importance. Improvement in processing accuracy such as high-aspect ratio and narrowing of the minimum line width is strongly required.
As one of such microfabrication techniques of semiconductor devices, reactive ion etching (RIE) is known. RIE allows anisotropic microfabrication processing with a high etching rate. Generally, in an RIE apparatus, a pair of electrodes are disposed facing each other with a predetermined space therebetween in a chamber where the atmosphere can be adjusted. A substrate is held onto one electrode and radio frequency (RF) electric power is supplied to the electrode to generate plasma between the electrodes.
RIE utilizes the mixture effect of physical etching (sputtering) and chemical etching. In physical etching, a potential difference between self-bias voltage generated on a substrate during generation of plasma and the potential of the plasma accelerates positive ions in the plasma. The accelerated positive ions are incident on the substrate and collide with it, so that etching proceeds. In chemical etching, etching proceeds due to active neutral radicals.
The plasma potential is relatively smaller than the self-bias voltage. Therefore, energy control of ions that are incident on the substrate is performed by controlling of the self-bias voltage.
The potential of the electrode periodically varies in accordance with the RF voltage, and therefore the ion energy also periodically varies. The ion energy distributes depending on the frequency of the RF voltage. The lower the frequency of the RF voltage is, the larger the distribution of the ion energy is.
When distribution is made in the ion energy, ions of high energy cause shoulder cutting of a pattern to degrade a processed shape. On the other hand, ions of low energy have a possibility of not contributing to processing of a substrate, or a possibility of degrading a processed shape due to deterioration of anisotropy. As disclosed in U.S. Patent Application No. 2004/0219797A1, a technique is proposed that uses RF electric power having two or more different frequencies that include RF electric power of a high frequency for generating and maintaining plasma and RF electric power of a low frequency for controlling ion energy.
In such a technique, the distribution of ion energy due to the low frequency is large. It is difficult to sufficiently narrow this distribution of ion energy to a range required for improvement in processing accuracy. Increasing the frequency of the RF electric power of the low frequency can reduce the distribution of ion energy. However, there is a problem that it becomes difficult to obtain desired ion energy.